When a camera is deployed to capture images, it is possible to determine real-world distances between different points in those images. To do so, the camera is first calibrated by estimating certain camera parameters. One way to calibrate a camera is to use real-world coordinates of known landmarks to derive the camera parameters. However, this approach can involve tremendous amounts of human effort, and also needs to be re-performed if the camera changes any pan, tilt, or zoom parameters.